I have recently answered a question on Quora.com about creativity. The question asked "What are the keys to feeding my creativity?" That set me up really well to talk about the two things that are most important to me, when it comes to finding inspiration. The answer was also published on Inc.com.

The answer went as follows:

Creativity is different for different people. Creatives acting in different areas will have different ways of feeding their creativity. A comedian, for instance, may feed his creativity by noticing everyday life events. A creative soccer player may feed his creativity by mimicking other great players.

Since your question didn't specify what kind of creative endeavor you're undertaking, I'll be very broad in my answer. Because, although inspiration can come from different sources for different people, there are basic concepts in creativity that hold true for any kind of scenario.
To me, the most important keys to inspiration are knowledge and action.

Knowledge

Creativity, by definition, involves creation. We have to remember that nothing is really created out of the blue. Every new idea emerges for some sort of combination between two or more pre-existing concepts.

By that logic, the more knowledge you have of pre-existing concepts, the greater the potential to create unique connections between those concepts. The knowledge you choose to acquire will definitely impact the kinds of ideas you're going to have.

Seek knowledge that you're interested in and/or is relevant to the area of creativity you're invested in. Also, having lots of unrelated general knowledge will boost your creativity as well.

Action

On the book "Accidental Creative" by Todd Henry I read the phrase:

"Action leads to inspiration, not the other way around."

That's absolutely true. Before I started writing this very text, I felt I wouldn't have much to say. But now that I'm in the middle of doing it, the juices are flowing and I'm thinking of a bunch of things I could say, and a bunch of ways to illustrate what I mean. Once I consciously overcame that feeling and pushed myself to write, I placed my mind in a creative space. Now it's moving. Now it's making connections and creating new things.

Start doing whatever it is you're trying to do. Don't wait for inspiration to grow out of thin air, or you'll never start. It is common for creative people to look at their own work when they're done and go "Wow, I didn't think I could do that!" That still happens to me a lot, and it's a great feeling. And you only get that feeling if you brave the blank canvas.

Knowledge and action have the potential to create a virtuous cycle of creativity: the more you know, the more you can do. The more you do, the more you want to know. If you keep feeding those fires, you can keep the inspiration train going.